One-part self-etching, self-priming dental adhesive compositions known from the prior art typically contain a mixture of an acid, a polymerizable monomer and an initiator system in a suitable solvent. The acidity of the mixture must be adapted to provide sufficient etching activity on dentin and enamel surfaces. However, an increased acidity leads to a complex stability problem due to the activation of chemical bonds of the functional components of the mixture. Specifically, ester bonds present in the polymerizable monomers may be solved under acid catalysis. Moreover, the initiator system may be activated in the acidic medium leading to premature polymerization of the mixture.
As a result of the stability problem of the mixture, the storage stability at room temperature of commercial one-part self-etching, self-priming dental adhesive compositions known from the prior art may be insufficient. Accordingly, conventional commercial one-part self-etching, self-priming dental adhesive compositions must be stored in a refrigerator in order to avoid deterioration by solvolysis or polymerization. As an Example, the commercial composition “iBond Gluma inside” may be mentioned, which has a low thermal stability when stored at temperatures of 37° C. or 50° C. due to premature polymerization within less than two weeks, which is indicative of an insufficient thermal stability at room temperature for all practical purposes.
EP-A 1 548 021 suggests hydrolysis stable one-part self-etching, self-priming dental adhesive compositions containing specific monomers having improved resistance against hydrolysis under acidic conditions. In order to improve the stability of the initiator system, EP-A 1 548 021 suggests a stabilizer such as hydroquinone monomethylether, 2,6-di-tert.-butyl-p-cresol, tetramethyl piperidine N-oxyl radical and galvanoxyl radical. However, generic one-part self-etching, self-priming dental adhesive composition known from EP-A 1 548 021 still require improvement of the thermal stability at storage for attaining a stability of at least 10 days at 60° C. required. Moreover, hydroquinone is an allergenic compound imparting undesirable toxic properties to a dental adhesive composition.